Various communications systems employ horn antenna structures for transmitting and/or receiving electromagnetic signals. A horn antenna structure typically includes a horn attached to or otherwise formed at the end of a waveguide. The horn shape affords a gradual transition to free space, which mitigates mismatch or reflections at the open end. The dimensions and configurations of the horn can be selected to produce a desired radiation pattern and a desired amount of antenna gain. The area of the output aperture (e.g., height times width) determines the amount of antenna gain the horn will exhibit. The larger the output aperture, the more gain the antenna will exhibit.
Traditionally, conical horns provided only the TE11 mode, where the E-plane beamwidth is substantially less than the H-plane beamwidth. Consequently, when such traditional horns were used to transmit or receive a circularly polarized signal, the signals were not sufficiently circularly polarized, but instead were elliptically polarized. Potter horns and corrugated horns were developed to reduce the axial ratio and provide a highly circularly polarized beam over a narrow bandwidth. The Potter and corrugated horns generate substantially equal E-plane and H-plane patterns with suppressed sidelobes. The Potter horn is a conical shaped feed horn that includes a single step transition that provides for the propagation of the TM11 mode for equal E-plane and H-plane beamwidths and suppressed sidelobes. The corrugated horn is a conical shaped feed horn that includes a corrugated structure within the horn from the waveguide to the aperture that also provides substantially equal E and H plane beamwidth and suppresses the sidelobes.
Waveguides having a circular or rectangular cross-section, which are referred to as circular or rectangular waveguides, respectively, are used in high frequency (HF) applications for transmitting HF signals. The interior space of a waveguide can be filled with air or with a solid dielectric material, for example. As noted above, an antenna, such as a horn or antenna, is arranged at one end of a waveguide for radiating or receiving HF signals relative to free space.
Present methods of feeding a multi-frequency horn antenna include a broadband feed structure that usually consists of many, multiple wavelength sections of waveguides. The multiple sections of waveguides are configured to couple from the waveguide to the feed to the antenna structure. Such feed mechanisms tend to be quite large volume since the feed structure dimensions depend on the frequency of the horn antenna structure. Additionally, the frequency range for such conventional feed structures may be limited because the entire feed structure is often required to cover multiple octave bandwidths simultaneously.